Deep Cerebellar Nuclei Play an Important Role in Two- Tone Discrimination on Delay Eyeblink Conditioning in C57BL/6 Mice

Previous studies have shown that deep cerebellar nuclei (DCN)-lesioned mice develop conditioned responses (CR) on delay eyeblink conditioning when a salient tone conditioned stimulus (CS) is used, which suggests that the cerebellum potentially plays a role in more complicated cognitive functions. In the present study, we examined the role of DCN in tone frequency discrimination in the delay eyeblink-conditioning paradigm. In the first experiment, DCN-lesioned and sham-operated mice were subjected to standard simple eyeblink conditioning under low-frequency tone CS (LCS: 1 kHz, 80 dB) or high-frequency tone CS (HCS: 10 kHz, 70 dB) conditions. DCN-lesioned mice developed CR in both CS conditions as well as sham-operated mice. In the second experiment, DCN-lesioned and sham-operated mice were subjected to two-tone discrimination tasks, with LCS+ (or HCS+) paired with unconditioned stimulus (US), and HCS2 (or LCS2) without US. CR % in sham-operated mice increased in LCS+ (or HCS+) trials, regardless of tone frequency of CS, but not in HCS2 (or LCS2) trials. The results indicate that sham-operated mice can discriminate between LCS+ and HCS2 (or HCS+ and LCS2). In contrast, DCN-lesioned mice showed high CR % in not only LCS+ (or HCS+) trials but also HCS2 (or LCS2) trials. The results indicate that DCN lesions impair the discrimination between tone frequency in eyeblink conditioning. Our result